U.S. patent application number 11/061143 was filed with the patent office on 2005-09-08 for diffusion barrier layer and method for manufacturing a diffusion barrier layer.
Invention is credited to Gallissian, Alice, Kharrazi-Olsson, Maryam, Tran Quoc, Hai.
Application Number | 20050194898 11/061143 |
Document ID | / |
Family ID | 34886254 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050194898 |
Kind Code |
A1 |
Kharrazi-Olsson, Maryam ; et
al. |
September 8, 2005 |
Diffusion barrier layer and method for manufacturing a diffusion
barrier layer
Abstract
A diffusion barrier system for a display device comprising a
layer system with at least two layers of dielectric material,
wherein at least two adjacent layers of that layer system comprise
the same material. A respective method for manufacturing such a
diffusion barrier system in a single process chamber of a plasma
deposition system has the steps of introducing a substrate to be
treated in said process chamber, discretely varying in a controlled
manner during deposition at least one process parameter in the
process chamber, without completely interrupting such process
parameter, which results in layers with different properties and
finally unloading said substrate from said process.
Inventors: |
Kharrazi-Olsson, Maryam;
(Buchs SG, CH) ; Tran Quoc, Hai; (Orsay, FR)
; Gallissian, Alice; (Cachan, FR) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET
SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Family ID: |
34886254 |
Appl. No.: |
11/061143 |
Filed: |
February 18, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60546274 |
Feb 20, 2004 |
|
|
|
Current U.S.
Class: |
313/512 |
Current CPC
Class: |
Y02P 70/50 20151101;
H01L 51/5256 20130101; Y02P 70/521 20151101; H01L 51/0097 20130101;
Y02E 10/549 20130101; H01L 51/5253 20130101; Y10S 428/917 20130101;
Y10T 428/325 20150115 |
Class at
Publication: |
313/512 |
International
Class: |
H01J 001/62; H01J
063/04 |
Claims
What is claimed is:
1. A diffusion barrier system for a display device comprising a
layer system with at least two layers of dielectric material,
wherein at least two adjacent layers of that layer system comprise
the same material.
2. Diffusion barrier system according to claim 1, wherein said
dielectric material is one of an nitride, oxide, carbide and
oxynitride or combinations thereof.
3. Diffusion barrier system according to claim 1, wherein said
dielectric material comprises a metal or a semiconductor.
4. Diffusion barrier system according to claim 3, wherein the metal
is one of Al, Cr, Cu, Ge, In, Ir Sb, Sn, Ta, Ti, Zr or combinations
thereof.
5. Diffusion barrier system according to claim 1, wherein the
dielectric material comprises silicon nitride or silicon oxynitride
(SiO.sub.xN.sub.y).
6. Diffusion barrier system according to claim 1 wherein the layer
thickness varies from 15-100 nm
7. Method for manufacturing a diffusion barrier system comprising
layers of dielectric material, in a single process chamber of a
plasma deposition system with the following steps: (1) Introducing
a substrate to be treated in said process chamber (2) Discretely
varying in a controlled manner during deposition at least one of
the process parameters in the process chamber gas flow, power,
pressure, temperature without completely interrupting such process
parameter, such that each variation results in a layer with
different properties (3) unloading said substrate from said process
chamber
8. Method according to claim 7, wherein the temperature is kept at
a value between 80.degree. C. and 175.degree. C.
9. Method according to claim 6, wherein the plasma process is a
physical vapor deposition (PVD) process or a plasma enhanced
chemical vapor deposition (PECVD) process.
10. Display device comprising a substrate chosen from the group of
glass, metal, polymer or paper with a diffusion barrier system
according to claim 1.
Description
FIELD OF THE INVENTION
[0001] A (solid state) ultra high diffusion barrier and
encapsulation layer for optoelectronic devices, consisting of
multiple inorganic layers, which are deposited by a single step
vacuum deposition process.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to optoelectronic
devices and more specifically to environmentally sensitive
optoelectronic devices. These devices include organic
optoelectronic devices such as organic light emitting diodes (OLED)
be it either small molecules or polymer type, organic photovoltaic
devices, organic thin film transistors, and organic electrochromic
displays, electrophoretic inks, solar devices, and LCD's in general
(including applications for watches, cell phones etc.).
[0003] Many such optoelectronic devices are known in the art.
However, specifically organic optoelectronic devices such as OLEDs
have not yet made their predicted significant economic and
technical breakthrough. This is partially due to the fact that the
organic structures and the cathodes need to be heavily protected
from the environment, specifically from oxygen, from water and from
water vapor.
[0004] Currently, many optoelectronic devices (such as LCD and OLED
displays) are manufactured by depositing thin film structures on a
glass substrate, which has excellent optical properties and which
is also an excellent environmental barrier. Most organic
optoelectronic devices today are also manufactured on glass
substrates and are encapsulated in glass (or in metallic-)
structures. By its brittle nature however, glass does not provide
flexibility and light weight. By using thin, flexible polymeric
substrates for OLEDs in particular--which is known in the art--and
by thin encapsulation layers for the device, a high degree of
flexibility and lightweight shall be obtained. However, the
following problems arise simultaneously:
[0005] Thin polymeric substrates and organic structures have a
diffusion coefficient for oxygen and for water, which is far to
high to protect the enclosed structures from degradation.
[0006] Thin polymeric substrates and organic structures are
susceptible to degradation, deformation and building up of
thermally induced stresses when the functional layers are deposited
due to the process temperature created intentionally or
unintentionally during the deposition.
[0007] For illustration, FIG. 1 shows the typical build up for an
organic optoelectronic device on an organic substrate: in order to
protect the device (here an OLED pixel with its electrodes) from
the environment, a barrier layer between the polymeric substrate
and the device, and an encapsulation layer covering the whole
device are necessary. FIG. 1 shows a cross section of an OLED
device, with an flexible substrate 1, a barrier layer 2, a
transparent conductive oxide (TCO) layer 3, OLED layer(s) 4
(organic), cathode 5 and encapsulation layer 6.
[0008] Both, the organic layers 4 and also the metallic cathode 6
need to be protected from oxygen and vapor diffusion, the market
requires that the device to be light weight and flexible, the
functional layers to be transparent for light of the desired
wavelength, the device to be easily manufacturable and the
functional layers to have excellent mechanical properties.
Additionally, the encapsulation layer 6 needs to offer some
mechanical and chemical stability, must seal off the device
hermetically and must closely fill the complex top structure of the
device during application of the film (step coverage).
[0009] Related Art
[0010] Encapsulation layers have been proposed previously as a
combination of a sputtered inorgaEnic layer such as AlOX, SiN, SiON
plus a polymer plus another inorganic layer (I-P-I structure).
Alternatively a stack, a sequence of I-P-I-P-I . . . layers have
been proposed to further improve the properties of the
encapsulation layer (system). In such an arrangement the inorganic
layer prevents the water diffusion while the organic layer have the
purpose to planarize the inorganic layer and to provide a new
smooth surface to deposit for the next inorganic layer. Pinhole-,
particle-, and step coverage are further important functions of the
organic layer.
[0011] In "Thin film encapsulation of OLED Displays with a NONON
Stack" (Lifka/va Esch/Rosink in: SID 04 Digest, p. 1384 ff) the
authors describe a sequence of SiN--SiO--SiN layers (NON) or,
widened about further layers of that kind as NONON layer. WO
03/050894 describes basically the same system with typical layer
thicknesses of 200 nm SiN, 300 nm SiO and again 200 nm of SiN.
Similar related Prior Art is described in U.S. Pat. No. 6,268,695,
U.S. Pat. No. 6,638,645, U.S. Pat. No. 6,576,351, U.S. Pat. No.
6,573,652, U.S. Pat. No. 6,597,111 and SID 2003, Baltimore,
Proceeding 21.1/A. Yoshida.
[0012] Since prior art uses a succession of multiple organic and
inorganic layers for the intended barriers, these stacks are
expensive and difficult to produce, because they require several
different process steps.
[0013] In consequence, a coating system suitable for such
applications must show several, independent, separable process
chambers. Besides the disadvantage of being costly for mass
production due to the low throughput, there is also the risk for
contamination during the transferring process from (process-)
chamber to chamber for the stack formation.
[0014] In stacks where organic and inorganic materials are layered
alternatingly, problems also arise due to the mismatch in
mechanical and chemical properties of organic and inorganic
materials: different thermal expansion coefficients, insufficient
adhesion on each other and many more.
[0015] In general, the chemical compatibility of such barrier
stacks with the OLED process is a matter of concern.
[0016] When glass or metal lids are alternatively used as an
environmental encapsulation, flexibility and lightweight is lost
and when single inorganic layers (such as silicon nitride layers)
are used, the requirements for permeability are not fulfilled.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows the typical build up for an organic
optoelectronic device on an organic substrate, comprising several
layers (Order from bottom to top: flexible substrate, barrier
layer, TCO (transparent conductive oxide) layer, OLED (organic
layers), cathode, and on top: encapsulation layer)
[0018] FIG. 2 shows the H.sub.2O permeation rate in grams per day
and square meter at 25 degrees Celsius for certain specifications
for OPV (organic photo voltaic) and OLED applications and on the
same scale typical permeation rates for certain state-of-the-art
coatings.
[0019] FIG. 3 shows a further embodiment of the invention.
[0020] FIG. 4 shows a scanning electron micrograph (SEM) with the
excellent step coverage of an inorganic layer according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present invention provides a diffusion barrier 2 and an
encapsulation layer 6 by depositing a set of multiple inorganic
layers (preferably of silicon nitride, SiN.sub.x) in a single step
vacuum deposition process.
[0022] FIG. 3 summarizes one embodiment of the present invention: A
flexible substrate 10 shows barrier layer(s) 11. A stack of
(multiple) inorganic layers 12 has been deposited, however shows,
due to the manufacturing process, pinhole defects 13 and particles
14. Each layer of layer stack 12 shields against the environment
independently and the average diffusion path lengths between
defects are increased significantly.
[0023] The solution of the invention is based on multiple inorganic
layers (preferably of silicon nitride). This plurality of layers is
deposited by an essentially single step PECVD process (i.e.
including only one loading/unloading operation into the process
chamber), directly on polymeric substrates (which are known in the
art) with hard coatings (which are also known in the art). By
essentially and discretely controlling the atmospheric conditions
(of NH.sub.3, H.sub.2, SiH.sub.4, N.sub.2) and other process
parameters such as process pressure, process power, and substrate
temperature during the single step PECVD deposition process,
several discrete layers of inorganic material are deposited.
[0024] These layers may thus discreetly vary, not only in their
stoechiometric composition, but also in the elements from which
they are composed.
[0025] The layers according to the present invention provide faster
packaging than prior art and must prevent damage to the device from
moisture and oxygen, thereby improving the lifetime of the device.
Such layers can also serve as "ultra high diffusion barrier" on
polymeric substrates to protect the stack from the attack of
moisture and gas through the substrate surface. In this case, the
process parameters are adjusted for each application, e.g.
encapsulation on the device side and diffusion barrier on the
polymeric substrate side or sides. However, in both cases,
conformal and defect-less layers at relatively low process
temperature are required to avoid mechanical deformation of the
substrate and damage to the temperature sensitive OLED device.
[0026] Due to the fact that multiple discrete layers are deposited
and present horizontally, the effect of defects (such as particles
14 and pinhole defects 13) are minimal perpendicular to the plane
of attack. Unwanted chemical agents such as oxygen and vapor
statistically find much less direct access paths across the
multilayer inorganic stacks than in a much thicker single layer
barrier with the same number of defects. This is why the diffusion
coefficient across such multilayer inorganic stacks is much lower
than across a single layer with the same overall thickness.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] In a first embodiment a diffusion barrier system for a
display device comprises a layer system with at least two layers of
dielectric material, wherein at least two adjacent layers of that
layer system comprise the same material. In a further embodiment
said dielectric material is one of an nitride, oxide, carbide and
oxynitride or combinations thereof. Said dielectric material may
comprise a metal or a semiconductor, and again the metal is one of
Al, Cr, Cu, Ge, In, Ir Sb, Sn, Ta, Ti, Zr or combinations thereof.
In a further preferred embodiment the dielectric material comprises
silicon nitride or silicon oxynitride (SiO.sub.xN.sub.y). A display
device with such diffusion barrier layer can be based on a
substrate chosen from the group of glass, metal, polymer or
paper.
[0028] Accordingly a method for manufacturing such a diffusion
barrier system in a single process chamber of a plasma deposition
system will have the steps of introducing a substrate to be treated
in said process chamber, discretely varying in a controlled manner
during deposition at least on of the process parameters in the
process chamber gas flow, power, pressure, temperature without
completely interrupting such process parameter, such that each
variation results in a layer with different properties. Finally the
substrate is removed from said process chamber.
EXAMPLE 1
Diffusion Barrier
[0029] In order to achieve a highly efficient diffusion barrier on
both sides of a polymer substrate, the following process parameters
have been chosen on a Unaxis KAI PECVD system for a stack of four
layers of silicon nitride on each side of the substrate:
1TABLE 1 Standard Standard Standard Standard Deposition Temp. flow
flow flow flow Pressure RF Power Step time Thickness rate [.degree.
C.] [sccm] [sccm] [sccm] [sccm] [mbar] [kW] [min] [nm] [.ANG./s] T
SiH4 NH3 N2 H2 p P t D D/t 175 80 600 500 750 0.7 700 2.35 100 6.45
175 80 600 500 500 0.7 650 2.46 100 6.01 175 80 600 500 750 0.7 700
2.35 100 6.45 175 80 600 500 500 0.7 650 2.46 100 6.01
[0030] For comparison, a single layer of silicon nitride with the
same overall thickness, has also been deposited on both sides of a
substrate with the following parameters:
2TABLE 2 Standard Standard Standard Standard Deposition Temp. flow
flow flow flow Pressure RF Power Step time Thickness rate [.degree.
C.] [sccm] [sccm] [sccm] [sccm] [mbar] [kW] [min] [nm] [.ANG./s] T
SiH4 NH3 N2 H2 p P t D D/t 175 80 600 500 750 0.7 700 10.2 400
6.45
[0031] While a glass substrate (used as a reference in the so
called "Ca test", see below) exhibited a water vapor transition
rate (WVTR) of 3.1.times.10.sup.-5, the multilayer silicon nitride
stack according to Table 1 showed a WVTR of 1.5.times.10.sup.4, and
the single layer stack according to Table 2 showed a WVTR of
6.84.times.10.sup.-3 g/m.sup.2/day at 20.degree. C. and at 50%
humidity.
[0032] The "Ca test" is a permeation test, which is based on the
corrosion of reactive metal films. This all-optical method is used
to quantify the water transmission rate of substrates provided with
high performance diffusion barriers and is known to those skilled
in the art.
[0033] A glass plate with a Calcium coating is glued to the test
substrate (such as polymeric substrates with or without diffusion
barrier layer and possibly also a reference glass substrate).
Calcium readily reacts with water and oxygen entering the test
substrate and becomes progressively transparent. This leads to a
change in the optical transmission of Ca coating, which can be
monitored in time. The change in the transmission of the cells is
then used to quantify effective permeation rates (WVTR). However,
with this method, the change in the WVTR is also due to the
penetration of water through the "glue" material. That is why a
reference glass substrate; which normally has a WVTR of
.about.1.times.10.sup.-6 is also tested.
[0034] Here the test glass showed a WVTR of
.about.3.times.10.sup.-5 and relative to the reference, the WVTR of
the polymeric substrate/barrier layer system is measured to
1.5.times.10.sup.4.
EXAMPLE 2
Encapsulation layer
[0035] In order to achieve a highly efficient encapsulation layer,
the parameters in Table 3 have been used. Note that the deposition
temperatures have been substantially reduced as not to damage the
organic structures to be encapsulated.
3TABLE 3 Standard Standard Standard Standard Deposition Temp. flow
flow flow flow Pressure RF Power Step time Thickness rate [.degree.
C.] [sccm] [sccm] [sccm] [sccm] [mb] [kW] [min] [nm] [.ANG./s] T
SiH4 NH3 N2 H2 p P t D D/t 120 80 600 500 750 0.7 700 2.35 100 6.45
120 80 600 500 500 0.7 650 2.46 100 6.01 120 80 600 500 750 0.7 700
2.35 100 6.45 120 80 600 500 500 0.7 650 2.46 100 6.01
[0036] The multilayer silicon nitride stack deposited at
120.degree. C. showed a WVTR of 5.66.times.10.sup.4. By adjusting
the process parameters, one can further reduce the permeation rates
to the same level or even lower than the values for 175.degree. C.
process without loss of functionality.
[0037] In a third example, the deposition temperature has further
been lowered to 80.degree. C. with promising results.
[0038] In a fourth example, silicon nitride (SiN.sub.x) and silicon
oxynitride (SiO.sub.xN.sub.y) layers are deposited alternatingly on
top of each other.
[0039] The preferred number n of inorganic layers according to the
invention is at least 2, with a preferred range of 2-10. Even more
layers may be useful, and can be adjusted according to specific
requirements. The thickness of each layer can vary between 15-100
nm (the upper limit can be adjusted according to specific
requirements). The values for x in SiN.sub.x range between 0 and
4/3.
[0040] By carefully designing a single run step PECVD deposition
process (single loading/unloading step and thus a single deposition
run step), a simple, economic and very effective encapsulation
layer and an environmental barrier has been found. Average water
permeation values of 1.5.times.10.sup.-4, and peak values as low as
9.times.10.sup.-5 gr/m.sup.2/day were thus achieved.
[0041] The barrier layers were prepared with different polymeric
substrate pre-treatment, such as cleaning in an ultrasonic bath in
order to reduce the particle concentration prior to the deposition,
since cracks and micro-cracks initiate at microscopic defect sites,
thereby, reducing the permeation rate and the mechanical
stability.
[0042] The layers according to the invention are transparent in the
visible range, which is a requirement for most structures of
optoelectronic devices.
[0043] Silicon nitride multilayer barriers are excellent, both from
the mechanical and form the processing standpoint. They are able to
resist cracking during OLED processing and possess excellent
foldability. The crack resistance of the layers is decisive, since
mechanical failure of the diffusion barriers will directly result
in a shortened lifetime of the device. The failure onset of the
layers according to the invention is equal to approx. 1.5% strain,
which enables a minimum achievable curvature radius of
approximately 34 mm for a 100 .mu.m thick substrate. Adhesion of
the layers to both glass and to polymeric substrates is found to be
very high. The analysis prove a very high tensile strength (2.5
GPa) and very high interfacial shear strength (230 MPa) for the
layers on polymer, indicating that a strong interface is created
during plasma deposition of the nitrides. The tensile failure of
the SiN.sub.x is coupled to that of the underlying hard coat.
Furthermore, the cohesion and adhesion of SiN.sub.x on polymeric
substrate with and without hard coat layer before and after
hydrothermal loading (1 h in water at RT) are found to be
essentially unchanged.
[0044] The multiple layers deposited by PECVD achieve excellent
step coverage for the covering of all patterned structures of the
OLED stack, and the layers retain high barrier properties. FIG. 4
illustrates in a scanning electron micrograph the excellent step
coverage of an inorganic layer according to the invention. Using a
PECVD single run multi layer process, complex structures are
covered perfectly.
[0045] The production of multilayer inorganic barrier is
reproducible, and provides high throughput and low risk for
contamination due to the single step process. The multilayer
provides no mechanical miss-match and is chemically and
mechanically stable.
[0046] Since the inorganic layers according to the present
invention are generally chemically very stable (unlike the
inorganic/organic stacks in prior art), excellent etching
resistance is achieved. The chemical compatibility of the prior art
diffusion barriers with the OLED processing is a matter of concern.
Alumina of prior art is not resistant against common etching
solutions and the adhesion between the organic and inorganic layer
fails easily for instance after processing steps (e.g. etching) and
after mechanical and thermal cycling. Due to the inherent stack
instability, mechanical failure of such stacks is inevitable.
[0047] In general, the properties of multilayer inorganic diffusion
barrier produced utilizing vacuum deposition technologies are far
superior to what can be achieved by multiple layers of
organic/inorganic foils & stacks as described in prior art.
* * * * *